The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Deceleration fuel cut off (DFCO) systems are used in powertrains to disable fuel to an internal combustion engine (ICE). DFCO is typically enabled while a driveline (e.g., transmission, driveshaft, axle, and wheels) is engaged to the ICE. This supports and prevents stalling of the ICE due to deceleration of a vehicle and contact between the wheels of the vehicle and a road surface.
DFCO is used for various reasons. DFCO may be used to provide deceleration (powertrain braking) force when an accelerator of a vehicle is not actuated (e.g., vehicle operator does not press on accelerator pedal). In high elevation (mountainous) areas and/or areas with large variations in elevation, DFCO is used to provide powertrain braking to avoid damage to friction brakes of a vehicle. Although fuel is disabled when DFCO is enabled, the ICE may continue to draw air into the cylinders of the ICE. The drawing of air into the cylinders, compression of the air, and expulsion of the air from the ICE applies a braking (i.e., negative) torque on the ICE and/or powertrain. As such, torque losses attributable to engine pumping (i.e., pumping losses) occur when DFCO is enabled.
DFCO may also be used to prevent damage to a catalytic converter. For example, a throttle position may be calibrated and fixed to provide a minimal amount of air per cylinder (APC) to an engine, thereby providing vehicle deceleration when traveling downhill. Due to the fixed throttle position and/or a manual pull down of a transmission (PRNDL) shifter (e.g., shift into a low gear, such as L1 or L2), the APC levels of the ICE can become too low and cause a misfire. A misfire refers to incomplete combustion of an air/fuel mixture in a cylinder of the engine. This misfire can result in fuel entering and igniting in an exhaust system, which increases temperature of a catalyst of the catalytic converter. Damage to the catalyst can occur when temperatures of the catalyst exceed a threshold. By using DFCO, fuel is disabled, which protects the catalyst from misfire events.
DFCO may also be used to increase fuel economy. The efficiency of a gasoline spark ignited engine can be low at minimum combustion (i.e. minimum air and fuel levels) because of the pumping losses and other factors. Disabling the fuel is more efficient than reducing the amount of fuel to an ICE.